Isopimaric acid is an important component of rosin or pine oleoresin. Its content in Pinus elliottii rosin is about 20%. The stable phenanthrene ring skeleton structure and unique exocyclic double bond of isopimaric acid endow it with multiple characteristics of chemical reactions. Therefore, separating and purifying isopimaric acid from typical pine oleoresin or rosin is important for the development and utilization of pimaric-type resin acids.
There are three known isodextropimaric acid, which is an isomer of isopimaric acid, separating and purifying methods: the “piperidine precipitation method,” the “maleic anhydride addition-isobutanolamine precipitation method” and the “distillation method”. In a report of Loeblich et al., isodextropimaric acid is separated by direct piperidine precipitation method and the yield of isodextropimaric acid is 4.7% (V. M. Loeblich and R. V. Lawrence, “A New Method for Isolating Isodextropimaric Acid From Pine Oleoresin and Rosin,” J. Org. Chem. 23(1):25-26 (1958)). This method directly separates the ammonium salt of isodextropimaric acid from raw material of rosin and the operation is simple. Its shortcoming is that although piperidine is selective to isodextropimaric acid, the crystallization rate of the generated ammonium salt of isodextropimaric acid is very low, the production cycle is long and the yield is low. Harris et al. removed abietic acid-type resin acids through a Diels-Alder addition reaction of maleic anhydride and then obtained isodextropimaric acid through selective precipitation of isobutanolamine. The yield of isodextropimaric acid is 8% (G. C. Harris and T. F. Sanderson, “Rosin Acids (III). The Isolation of Dextropimaric Acid, A New Pimaric-Type Acid, Isodextropimaric Acid,” J. Am. Chem. Soc. 70(1):2079-2085 (1948)). In this method, it is difficult to separate maleopimaric acid and unreacted resin acids (including pimaric-type resin acids, dehydro-abietic acid and a small amount of abietic acid-type resin acid that is not thoroughly reacted), and the separated unreacted resin acids may contain maleopimaric acid. Harris et al. also adopted a distillation method to directly evaporate pimaric acid and isodextropimaric acid and then used isobutanolamine to separate isodextropimaric acid. The yield relative to rosin is 4% (G. C. Harris and T. F. Sanderson, “Rosin Acids (III). The Isolation of Dextropimaric Acid, A New Pimaric-Type Acid, Isodextropimaric Acid,” J. Am. Chem. Soc. 70(1): 2079-2085 (1948)). This method has a high requirement for fractionation conditions; in addition, the operation is not easy and the yield of isodextropimaric acid is low.
At present, there are few domestic reports on the research of the separation and purification of isopimaric acid and no industrial-grade high-purity isopimaric acid products. Therefore, the exploration on the methods for separating isopimaric acid with high efficiency, high yield and high economic feasibility will accelerate the application of isopimaric acid in medical, biological, material and other fields.